They didn't and asking for sources on this forum is like asking a kid to hand over his doughnut. Not gonna happen.

No one really knows where the line between the old team and the new team is. We know for a fact that the new team was responsible for changing the direction of the gameplay. However, they used tons of assets that were already created over the past year and a half. It's not unlikely that the doomsday storyline was already being crafted before Yoshida took over.